Sterilization Using Plasma Generated NOx

ABSTRACT

Systems and methods for plasma sterilization are described. The sterilization method includes placing a substance to be sterilized into a rotating chamber and irradiating the substance with plasma. An RF generator is used to produce the plasma from a gas. The gas has a concentration of at least 85% N 2  and less than 15% O 2 . The plasma includes a NOx species that is effective in killing microbial organisms in the substance.

This application claims priority to U.S. provisional patent applicationNo. 61/718,493 filed on Oct. 25, 2012, U.S. provisional patentapplication No. 61/569,485 filed on Dec. 12, 2011, and U.S. provisionalpatent application No. 61/569,449 filed on Dec. 12, 2011. This and allother referenced extrinsic materials are incorporated herein byreference in their entirety. Where a definition or use of a term in areference that is incorporated by reference is inconsistent or contraryto the definition of that term provided herein, the definition of thatterm provided herein is deemed to be controlling.

FIELD OF THE INVENTION

The field of the invention is plasma sterilization.

BACKGROUND

The following description includes information that may be useful inunderstanding the present invention. It is not an admission that any ofthe information provided herein is prior art or relevant to thepresently claimed invention, or that any publication specifically orimplicitly referenced is prior art.

While numerous sterilization processes and devices are known, most arenot well suited for sterilizing food powder and other food-basedmaterials. This is due, in part, to the fact that food material issensitive and easily damaged (e.g., its composition can be easilychanged).

U.S. Pat. No. 4,133,638 to Healey discloses sterilization of powders,such as talc, by fluidizing a bed of the powder with a sterilizingstream of gas. A commonly used sterilizing agent is ethylene oxide, butbecause of its inflammatory and explosive nature it is often mixed witha compound, usually a fluorinated hydrocarbon, to render it is lessdangerous. A major problem, however, is that purchasing and transportingsterilization gases can be expensive.

U.S. patent application Ser. No. 10/585,088 to Arnold et al. (publishedas US2008/0317626) describes systems and methods that generate NO or amixture of NO and NO₂ as sterilization gases in situ, using acarbon-based diazeniumdiolate compound and a powdered acid. Thatprocess, however, is inconvenient and expensive.

Given the state of the art, there is still a need for improved gases forsterilization processes.

SUMMARY OF THE INVENTION

The inventive subject matter provides apparatus, systems and methods inwhich a sterilization apparatus employs reactive nitrogen species (RNS)to sterilize a substance (e.g., food powder, food-based materials,pharmaceutical compounds, etc.). The RND is produced in situ using aradio frequency (RF) generator. The RF generator converts a gas intoplasma having the RNS, which is then mixed with a substance to besterilized. In some embodiments, the mixing occurs in a rotating chamber(e.g., drum).

In a preferred embodiment the RNS comprises one or more NO_(x) species,especially mono-nitrogen oxides NO and NO2 (nitric oxide and nitrogendioxide), where the Nitrogen and Oxygen are derived from ambient air.

From a methods perspective the inventive subject matter includes thesteps of placing the substance in a rotating chamber, using an RFgenerator to produce a plasma, and subjecting the substance to theplasma (e.g., allowing the plasma to mix with the substance inside therotating chamber). In a preferred embodiment the plasma includes an RNSsuch as a NO_(x) species.

Various objects, features, aspects and advantages of the inventivesubject matter will become more apparent from the following detaileddescription of preferred embodiments, along with the accompanyingdrawing figures in which like numerals represent like components.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing of one embodiment of a sterilization system.

DETAILED DESCRIPTION

The following discussion provides many example embodiments of theinventive subject matter. Although each embodiment represents a singlecombination of inventive elements, the inventive subject matter isconsidered to include all possible combinations of the disclosedelements. Thus if one embodiment comprises elements A, B, and C, and asecond embodiment comprises elements B and D, then the inventive subjectmatter is also considered to include other remaining combinations of A,B, C, or D, even if not explicitly disclosed.

FIG. 1 shows a sterilization system 100. System 100 comprises a reactor101 and an RF generator 102. Reactor 101 is a drum that has an internalchamber with a substance 103 disposed inside. Substance 103 can compriseany substance that a user desires to sterilize via a plasmasterilization process. In some embodiments substance 103 is a food-basedmaterial such as a food powder.

Reactor 101 has a porous wall 104 through which gas 160 passes to enterthe internal chamber of reactor 101. Once inside the chamber, gas 160 isconverted into plasma 106 by RF generator 102 and coils 150. As reactor101 rotates in direction 110, plasma 106 and substance 103 mix. Reactivegroups in plasma 106 are effective in killing microbial organisms insubstance 103.

Plasma production and plasma sterilization processes are discussed infurther detail in U.S. Pat. No. 4,756,882 and co-pending applicationSer. No. 13/711,867 (filed on Dec. 12, 2012), which are incorporatedherein by reference.

In some embodiments, plasma 106 includes a NO_(x) species at aconcentration of at least 5%-10%, inclusive.

Gas 160 can comprise any gas suitable for plasma sterilization. In someembodiments, gas 60 can comprise air. In especially preferredembodiments, the gas 160 contains 85%-90% N₂ and between 10%-15% O₂, orbetween 87%-93% N₂, and between 13%-7% O₂. Since dry air containsroughly (by volume) 78% nitrogen, 21% oxygen, additional nitrogen can beprovided to air from an external source such as a bottle containingcompressed nitrogen.

Unless the context dictates the contrary, all ranges set forth hereinshould be interpreted as being inclusive of their endpoints andopen-ended ranges should be interpreted to include only commerciallypractical values. Similarly, all lists of values should be considered asinclusive of intermediate values unless the context indicates thecontrary. Still further, unless the context dictates the contrary, allconcentration percentages are to be interpreted as wt %.

In some embodiments, RF generator 102 is operated at powers from 100Watts to 5 kW, using a basic frequency of 13.56 MHz, while gas 160comprising 90% N₂ and 10% O₂ is supplied to reactor 101 at a total gasflow from 250 cc/m to 2000 cc/m, with reactor 101 having a chamberpressure in the range of 100 mTorr to 5 Torr.

As used herein, and unless the context dictates otherwise, the term“coupled to” is intended to include both direct coupling (in which twoelements that are coupled to each other contact each other) and indirectcoupling (in which at least one additional element is located betweenthe two elements). Therefore, the terms “coupled to” and “coupled with”are used synonymously.

As used in the description herein and throughout the claims that follow,the meaning of “a,” “an,” and “the” includes plural reference unless thecontext clearly dictates otherwise. Also, as used in the descriptionherein, the meaning of “in” includes “in” and “on” unless the contextclearly dictates otherwise.

The recitation of ranges of values herein is merely intended to serve asa shorthand method of referring individually to each separate valuefalling within the range. Unless otherwise indicated herein, eachindividual value is incorporated into the specification as if it wereindividually recited herein. All methods described herein can beperformed in any suitable order unless otherwise indicated herein orotherwise clearly contradicted by context. The use of any and allexamples, or exemplary language (e.g. “such as”) provided with respectto certain embodiments herein is intended merely to better illuminatethe invention and does not pose a limitation on the scope of theinvention otherwise claimed. No language in the specification should beconstrued as indicating any non-claimed element essential to thepractice of the invention.

Groupings of alternative elements or embodiments of the inventiondisclosed herein are not to be construed as limitations. Each groupmember can be referred to and claimed individually or in any combinationwith other members of the group or other elements found herein. One ormore members of a group can be included in, or deleted from, a group forreasons of convenience and/or patentability. When any such inclusion ordeletion occurs, the specification is herein deemed to contain the groupas modified thus fulfilling the written description of all Markushgroups used in the appended claims.

It should be apparent to those skilled in the art that many moremodifications besides those already described are possible withoutdeparting from the inventive concepts herein. The inventive subjectmatter, therefore, is not to be restricted except in the spirit of theappended claims. Moreover, in interpreting both the specification andthe claims, all terms should be interpreted in the broadest possiblemanner consistent with the context. In particular, the terms “comprises”and “comprising” should be interpreted as referring to elements,components, or steps in a non-exclusive manner, indicating that thereferenced elements, components, or steps may be present, or utilized,or combined with other elements, components, or steps that are notexpressly referenced. Where the specification claims refers to at leastone of something selected from the group consisting of A, B, C . . . andN, the text should be interpreted as requiring only one element from thegroup, not A plus N, or B plus N, etc.

What is claimed is:
 1. A method of sterilizing a substance, comprising:placing the substance in a rotating chamber; using an RF generator toproduce a plasma from a gas, wherein the gas has a concentration of atleast 85% N₂ and less than 15% O₂ and wherein the plasma comprises aNO_(x) species; and subjecting the substance to the NO_(x) species. 2.The method of claim 1, wherein the gas comprises 85%-90% N₂, inclusive,and 10%-15% O₂, inclusive.
 3. The method of claim 1, wherein the gascomprises 87%-93% N₂, inclusive, and 13%-7% 0 ₂, inclusive.
 4. Themethod of claim 1, wherein the gas comprises 89%-90% N₂ and 9%-10% O₂,inclusive.
 5. The method of claim 1, wherein the gas comprises 0.2%-1%Argon, inclusive.
 6. The method of claim 1, further comprisingsubjecting the substance to the NO_(x) species through pores in a wallof the chamber.
 7. The method of claim 1, further comprising, operatingthe RF generator at a basic frequency of 0.44 MHz to 27.12 MHz toproduce the plasma.
 8. The method of claim 7, further comprisingoperating the RF generator at a basic frequency of 13.56 MHz to producethe plasma.
 9. The method of claim 7, further comprising operating theRF generator at a basic frequency of 2-5 MHz to produce the plasma. 10.The method of claim 7, further comprising, operating the RF generator ata power between 100 Watts and 5 KW, inclusive, to produce the plasma.11. An apparatus for sterilizing a substance, comprising: a rotatingchamber having a lumen; and an RF generator configured to produce aplasma within or in the vicinity of the chamber, the plasma yielding aNO_(x) species in sufficient quantities to sterilize an amount of thesubstance within the lumen.
 12. The apparatus of claim 11, furthercomprising a source of gas for producing the plasma comprising 87%-93%N₂, inclusive, and 13%-7% O₂, inclusive.
 13. The apparatus of claim 11,further comprising a source of gas for producing the plasma comprising85%-90% N₂, inclusive, and 10%-15% O₂, inclusive.
 14. The apparatus ofclaim 11, further comprising a source of gas for producing the plasmacomprises 89%-90% N₂ inclusive, and 9%-10% O₂, inclusive.
 15. Theapparatus of claim 11, further comprising a source of gas for producingthe plasma comprises 0.2%-1% Argon, inclusive.
 16. The apparatus ofclaim 11, wherein the chamber has a porous wall through which the NO_(x)species can pass.
 17. The apparatus of claim 11, wherein the RFgenerator is configured to operate at a basic frequency of 0.44 MHz to27.12 MHz, inclusive.
 18. The apparatus of claim 17, wherein the RFgenerator is configured to operate at a basic frequency of 13.56 MHz.19. The apparatus of claim 17, wherein the RF generator is configured tooperate at a basic frequency of 2-5 MHz.
 20. The apparatus of claim 17,wherein the RF generator is configured to operate at a power between 100Watts and 5 KW, inclusive.